1. Field of the Invention
The present invention relates to a novel adsorbent for carbon monoxide. More particularly, the present invention is concerned with an adsorbent for carbon monoxide, comprising a composite comprised of a porous inorganic carrier and, carried thereon, a binary complex of a copper(I) halide and a nitrogen-containing compound selected from the group consisting of (a) at least one pyridine compound selected from pyridine and a derivative thereof and (b) a specific diamine. The adsorbent of the present invention can be produced by a method comprising contacting the porous inorganic carrier with a solution of the above-mentioned binary complex of the nitrogen-containing compound and the copper(I) halide in an organic solvent for the binary complex. The adsorbent of the present invention is advantageous not only in that by contacting a gaseous mixture containing carbon monoxide with the adsorbent, the carbon monoxide can be separated from the gaseous mixture, but also in that by desorbing and releasing carbon monoxide from the adsorbent having adsorbed thereon carbon monoxide into a carbon monoxide-depleted gas, a gaseous mixture having an increased concentration of carbon monoxide can be obtained. Further, even when the adsorbent of the present invention is unintendedly caused to contact an oxygen-containing gas, such as the air, by an operational error or the like, so that the adsorbent is deteriorated to have a poor adsorptive and desorptive ability for carbon monoxide, the adsorptive ability and desorptive ability of the deteriorated adsorbent can be recovered by treating the deteriorated adsorbent with a reducing agent.
2. Prior Art
Carbon monoxide has a wide variety of uses, for example, as a fuel, as a material for the synthesis of organic compounds, as a reducing agent for the reduction of minerals, and the like. Carbon monoxide is also used as one of the main materials in a field which is generally called "C.sub.1 chemistry".
Carbon monoxide is produced in the form of the so-called synthetic gas which is produced from coal, petroleum, natural gas or the like by a partial oxidation method, a steam-reforming method or the like. Carbon monoxide is also contained in a by-product gas and an off-gas, which are generated in ironworks and a petroleum refinery, respectively. In the above-mentioned cases, carbon monoxide is obtained in the form of a gaseous mixture thereof with hydrogen, nitrogen, carbon dioxide, methane, oxygen and the like. In many cases, such a gaseous mixture is saturated with water. Therefore, for obtaining carbon monoxide usable as a material in the chemical industry, it is necessary to separate carbon monoxide from the above-mentioned gaseous mixture.
The separation of carbon monoxide from the gaseous mixture can be conducted by an adsorptive separation method, such as a pressure-swing method or a temperature-swing method. The pressure-swing method is a method in which a gaseous mixture containing carbon monoxide is contacted with an adsorbent for carbon monoxide to adsorb the carbon monoxide thereon, and the resultant adsorbent having adsorbed thereon carbon monoxide is exposed to a reduced pressure atmosphere so as to cause the carbon monoxide to be desorbed and separated from the adsorbent. The temperature-swing method is a method in which a gaseous mixture containing carbon monoxide is contacted with a adsorbent for carbon monoxide to adsorb the carbon monoxide thereon, and the resultant adsorbent having adsorbed thereon carbon monoxide is subjected to heat treatment so as to cause the carbon monoxide to be desorbed and separated from the adsorbent.
Heretofore, various types of adsorbents have been proposed in connection with the separation of carbon monoxide from a gaseous mixture containing carbon monoxide by the pressure-swing method or the temperature-swing method.
For example, a solid adsorbent has been proposed which is obtained by a method comprising adding a copper(I) halide or copper(I) oxide to a solvent followed by stirring to obtain a solution or a suspension, adding activated carbon to the solution or the suspension to obtain a mixture, and removing the solvent from the obtained mixture by evacuation, distillation or the like. (see, for example, Unexamined Japanese Patent Application Laid-Open Specification Nos. 58-156517 and 59-105841).
Another solid adsorbent has been proposed which is obtained by a method comprising adding a copper(II) halide or a copper(II) oxide to a solvent followed by stirring to obtain a solution or a suspension, adding activated carbon to the solution or the suspension to obtain a mixture, removing the solvent from the obtained mixture by evacuation, distillation or the like to thereby obtain a solid, and optionally, treating the obtained solid with a reducing gas (see, for example, Unexamined Japanese Patent Application Laid-Open Specification Nos. 59-69414 and 59-136134).
Still solid adsorbent has been proposed which is obtained by a method comprising contacting a carrier selected from silica, alumina or silica-alumina with a solution of copper(I) chloride in a solvent therefor, and removing the solvent from the resultant mixture, or obtained by a method comprising heating the above-mentioned carrier, and contacting the heated carrier with a solution of copper(I) chloride in a relatively small amount of the solvent (see, for example, Unexamined Japanese Patent Application Laid-Open Specification Nos. 61-263635 and 62-113710).
A further solid adsorbent has been proposed which is obtained by a method comprising adding copper(I) chloride and aluminum(III) halide to a solvent followed by stirring to obtain a solution, adding activated carbon to the obtained solution to obtain a mixture, and removing the solvent from the obtained mixture by evacuation, distillation or the like (see, for example, Unexamined Japanese Patent Application Laid-Open Specification No. 58-124516).
Still a further solid adsorbent has been proposed which is obtained by a method comprising adding a resin having pyridyl groups and a copper(I) halide and/or copper(I) thiocyanate to a solvent followed by stirring to obtain a solution, and removing the solvent from the obtained solution by distillation under reduced pressure (see, for example, Unexamined Japanese Patent Application Laid-Open Specification No. 63-4845).
Still a further solid adsorbent which is obtained by a method comprising contacting a macroreticular type polystyrene having at least one amino group selected from a primary amino group, a secondary amino group and a tertiary amino group with a solution of a copper(I) halide in a solvent, and removing the solvent from the resultant mixture (see, for example, Examined Japanese Patent Application Publication No. 6-9651).
However, when the above-mentioned conventional solid adsorbent are used for separation of carbon monoxide, various problems inevitably arise, as described below.
The method in which use is made of an adsorbent comprising activated carbon and, carried thereon, a copper(I) halide, copper(I) oxide, a copper(II) salt or copper(II) oxide, has disadvantages in that the carbon monoxide adsorptive ability of the adsorbent is low, and that, when this method is used for separating carbon monoxide by adsorption from a gaseous mixture of carbon monoxide and carbon dioxide, the adsorbent used in this prior art is likely to adsorb carbon dioxide together with carbon monoxide, so that the adsorptive separation of carbon monoxide cannot be performed with high selectivity. In addition, in this method, when a copper(I) halide is contained in the adsorbent, hydrochloric acid is necessarily used as a solvent in the production of the adsorbent, so that the production equipment suffers vigorous corrosion.
The method in which use is made of an adsorbent comprising silica, alumina or silica-alumina and, carried thereon, copper(I) chloride, has disadvantages in that the adsorptive ability of the adsorbent is low, and that hydrochloric acid is necessarily used as a solvent in the production of the adsorbent, so that the production equipment suffers vigorous corrosion. When the adsorbent used in this method is produced by a method in which a relatively small amount of the solvent is used, and a copper(I) chloride solution is contacted with a carrier which has been preliminarily heated, the adsorbent has an improved adsorptive ability for carbon monoxide; however, the adsorbent has a disadvantage in that it becomes difficult to desorb carbon monoxide from the adsorbent by vacuum treatment.
The method in which use is made of an adsorbent comprising activated carbon and, carried thereon, a binary complex of copper(I) chloride and aluminum(III) chloride, has disadvantages in that the binary complex of copper(I) chloride and aluminum(III) chloride reacts, although slowly, with water contained in a gaseous mixture treated by the adsorbent, so that the binary complex is likely to be deactivated to lose the adsorptive activity and generates hydrogen chloride. For suppressing the deactivation of the binary complex and removing the generated hydrogen chloride, it is necessary to place a dehumidifying agent bed and a hydrogen chloride removal tower, respectively, on the upstream and downstream sides of the adsorbent bed, relative to the flow direction of the gaseous mixture.
The method in which use is made of an adsorbent comprising a pyridyl group-containing resin and copper(I) halide and/or copper(I) thiocyanate, has disadvantages in that the production of the pyridyl group-containing resin needs high cost and, hence, the adsorbent produced using the pyridyl group-containing resin inevitably becomes expensive, and that the pyridyl group is chemically bonded to the polymer, so that the pyridyl group cannot easily coordinate to the copper(I) ion, leading to a lowering in the carbon monoxide adsorptive ability of the absorbent.
The method in which use is made of an adsorbent comprising a macroreticular polystyrene resin having at least one amino group selected from the group consisting of a primary amino group, a secondary amino group and a tertiary amino group, and a copper(I) halide coordinated to the polystyrene resin, has disadvantages in that the production of the amino group-containing resin needs high cost and, hence, the adsorbent produced using the amino group-containing resin inevitably becomes expensive, and that the amino group is chemically bonded to the polymer, so that the amino group cannot easily coordinate to the copper(I) ion, leading to a lowering in the carbon monoxide adsorptive ability of the adsorbent.